The evolution of radio access schemes and radio networks for cellular mobile communication (hereinafter referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”) has been standardized by the 3rd Generation Partnership Project (3GPP). In LTE, an Orthogonal Frequency Division Multiplexing (OFDM) scheme, which is a multi-carrier transmission method, is used as a communication scheme for radio communication from a base station device to a mobile station device (downlink; called DL). In LTE, furthermore, an SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme, which is a single-carrier transmission method, is used as a communication scheme for radio communication from a mobile station device to a base station device (uplink; called UL). In LTE, a DFT-Spread OFDM (Discrete Fourier Transform-Spread OFDM) scheme is used as the SC-FDMA scheme.
In 3GPP, a radio access scheme and a radio network (hereinafter referred to as “Long Term Evolution-Advanced (LTE-A)” or “Advanced Evolved Universal Terrestrial Radio Access (A-EUTRA)”) that implement data communication at a higher speed than that of LTE are under study. In LTE-A, there is a demand for backward compatibility with LTE. In LTE-A, it is requested that an LTE-A-enabled base station device simultaneously communicate with an LTE-A-enabled mobile station device and an LTE-enabled mobile station device, and that an LTE-A-enabled mobile station device communicate with an LTE-A-enabled base station device and an LTE-enabled base station device.
In LTE-A, to meet the request, at least supporting of the same channel structure as that of LTE is under study. The term “channel” means a medium used for the transmission of signals. A channel used in the physical layer is referred to as a physical channel, and a channel used in the Medium Access Control (MAC) layer is referred to as a logical channel. Types of physical channels include a physical downlink shared channel (PDSCH) used for the transmission and reception of downlink data and control information, a physical downlink control channel (PDCCH) used for the transmission and reception of downlink control information, a physical uplink shared channel (PUSCH) used for the transmission and reception of uplink data and control information, a physical uplink control channel (PUCCH) used for the transmission and reception of control information, a synchronization channel (SCH) used for the establishment of downlink synchronization, a physical random access channel (PRACH) used for the establishment of uplink synchronization, and a physical broadcast channel (PBCH) used for the transmission of downlink system information. A mobile station device or a base station device maps and transmits signals generated from control information, data, and the like on the respective physical channels. The data transmitted on the physical downlink shared channel or the physical uplink shared channel is referred to as a transport block.
The control information mapped on the physical uplink control channel is referred to as uplink control information (UCI). The uplink control information is control information (reception acknowledgement response; ACK/NACK) indicating a positive response (Acknowledgement: ACK) or a negative response (Negative Acknowledgement: NACK) to received data mapped on the physical downlink shared channel, or control information (Scheduling Request: SR) indicating a request for the allocation of uplink resources, or control information (Channel Quality Indicator: CQI) indicating the reception quality (also referred to as channel quality) in the downlink.
<Coordinated Communication>
In A-EUTRA, inter-cell coordinated communication (Cooperative Multipoint: CoMP communication) is under study in which neighboring cells coordinate with each other to perform communication in order to reduce or suppress interference with a mobile station device in the cell-edge area or in order to increase the received signal power. For example, a form of base station device that performs communication using an arbitrary frequency band is referred to as a “cell”. For example, inter-cell coordinated communication of a type in which different weighted signal processing (precoding processing) methods are applied to a signal in a plurality of cells and a plurality of base station devices coordinate with each other to transmit a signal to the same mobile station device (also referred to as Joint Processing or Joint Transmission) and the like are under study. This method may increase the signal power to interference plus noise power ratio of the mobile station device, and may improve the reception performance of the mobile station device. For example, inter-cell coordinated communication of a type in which a plurality of cells coordinate with each other to perform scheduling for a mobile station device (Coordinated Scheduling: CS) is under study. This method may increase the signal power to interference plus noise power ratio of the mobile station device. For example, inter-cell coordinated communication of a type in which a plurality of cells coordinate with each other to apply beamforming to transmit a signal to a mobile station device (Coordinated beamforming: CB) is under study. This method may increase the signal power to interference plus noise power ratio of the mobile station device. For example, inter-cell coordinated communication of a type in which a signal is transmitted on only one cell using a certain resource while no signal is transmitted on the other cell using a certain resource (Blanking, Muting) is under study. This method may increase the signal power to interference plus noise power ratio of the mobile station device.
As for a plurality of cells used for coordinated communication, different cells may be configured by different base station devices, or different cells may be configured by different RRHs (Remote Radio Heads, each of which is an outdoor radio unit smaller than a base station device, also referred to as Remote Radio Unit: RRU) managed by the same base station device. Alternatively, different cells may be configured by a base station device and an RRH managed by the base station device, or different cells may be configured by a base station device and an RRH managed by another base station device different from the base station device.
A base station device with a wide coverage is generally referred to as a macro base station device. A base station device with a narrow coverage is generally referred to as a pico base station device or a femto base station device. Application of an RRH in an area that generally has a narrower coverage than a macro base station device is under study. A deployment like a communication system including a macro base station device and an RRH and configured such that the coverage supported by the macro base station device includes part or all of the coverage supported by the RRH is referred to as a heterogeneous-network deployment. A communication system with such a heterogeneous-network deployment in which a macro base station device and an RRH coordinate with each other to transmit signals to a mobile station device located in an overlapped coverage area is under study. The RRH is managed by the macro base station device, and its transmission and reception are controlled. The macro base station device and the RRH are connected via a wired line such as a fiber optic line or a wireless line that is based on relay technology. In this way, the macro base station device and the RRH execute coordinated communication using radio resources some or all of which are identical, thereby improving the total spectral efficiency (transmission capacity) within the area of the coverage established by the macro base station device.
A mobile station device can perform single-cell communication with a macro base station device or an RRH while located near the macro base station device or the RRH. That is, a given mobile station device communicates with a macro base station device or an RRH without using coordinated communication, and transmits and receives signals. For example, a macro base station device receives an uplink signal from a mobile station device that is close to the macro base station device. For example, an RRH receives an uplink signal from a mobile station device that is close to the RRH. In addition, while located near the edge (cell edge) of the coverage established by the RRH, the mobile station device needs to take measures against co-channel interference from a macro base station device. Multi-cell communication (coordinated communication) between the macro base station device and the RRH with the use of a CoMP scheme in order to reduce or suppress interference with a mobile station device in the cell-edge area is under study. In the CoMP scheme, neighboring base stations coordinate with each other.
Also under study is a mobile station device that receives signals transmitted from both a macro base station device and an RRH using coordinated communication in the downlink, and that transmits a signal in a form suitable for either a macro base station device or an RRH in the uplink. For example, a mobile station device transmits an uplink signal at a transmit power suitable for a macro base station device to receive the signal. For example, a mobile station device transmits an uplink signal at a transmit power suitable for an RRH to receive the signal. Accordingly, unnecessary uplink interference may be reduced and spectral efficiency may be increased.
Also under study is a mobile station device that estimates a path loss from each of a plurality of types of reference signals to set a transmit power parameter suitable for a macro base station device or an RRH to receive a signal (NPL 1). For example, a mobile station device calculates a transmit power parameter suitable for a macro base station device to receive a signal, using a reference signal transmitted from the macro base station device. For example, a mobile station device calculates a transmit power parameter suitable for an RRH to receive a signal, using a reference signal transmitted from the RRH. For example, a mobile station device calculates a transmit power parameter that is suboptimal for a macro base station device or an RRH to receive a signal, using a reference signal transmitted from both the macro base station device and the RRH in a coordinated way. Specifically, a mobile station device performs path loss estimation on the basis of the reception quality of a received reference signal.
Further, a mobile station device notifies a base station device of power headroom (PH) so that the base station device can recognize how much transmit power the mobile station device has left to transmit an uplink signal until a maximum transmit power value (allowable maximum transmit power value) that the mobile station device can use as the device capability is reached. The power headroom (PH) is given by subtracting a transmit power value used for the transmission of an uplink signal from the maximum transmit power value.
The power headroom shows a value in the range of −23 dB to 40 dB, and is represented in units of 1 dB. Power headroom with a positive value indicates that the mobile station device has transmit power left. A power headroom with a negative value indicates that the mobile station device is in transmission state with the allowable maximum transmit power value although the mobile station device has been requested by a base station device to perform transmission with a transmit power value exceeding the allowable maximum transmit power value. The base station device adjusts and determines the frequency bandwidth of resources to be allocated to an uplink signal of the mobile station device, the modulation scheme of the uplink signal, and so on using information on the power headroom.
The mobile station device controls power headroom transmissions using two timers (periodicPHR-Timer and prohibitPHR-Timer) and one value dl-PathlossChange (expressed in dB) that are notified by the base station device. The mobile station device determines that power headroom will be transmitted if any of the following events occurs. The first event is that “prohibitPHR-Timer has expired and the value of the path loss has changed dl-PathlossChange [dB] or more from the value of the path loss used for calculation in the previous power headroom transmission”. The second event is that “periodicPHR-Timer has expired”. The third event is “the configuration or reconfiguration of the power headroom transmission functionality”. In this manner, a process for determining whether or not to transmit the power headroom and sending a power headroom report to a base station device is referred to as power headroom reporting.
The mobile station device determines that power headroom will be transmitted, and transmits an uplink signal including information concerning the power headroom to the base station device upon allocation of resources to be used for the transmission of the uplink signal by the base station device. Upon transmitting the information concerning the power headroom, the mobile station device once resets the periodicPHR-Timer timer and the prohibitPHR-Timer timer that are in measurement mode, and restarts the periodicPHR-Timer timer and the prohibitPHR-Timer timer.